Apparatus for drilling boreholes



May 25, 1965 H. ROBINSON, JR

APPARATUS FOR DRILLING BOREHOLES 2 Sheets-Sheet 1 Filed May 27, 1963 FIRING PIN EXPLOSIVE FIG. 2,

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APPARATUS FOR DRILLING BOREHQLES Filed May 27, 1963 2 Sheets-Sheet 2 DRILL l n PIPE 3 j 5 APSULE I T |3A i DRILLlNGA FIG. 5.

INVENTO FORMATION LEON H.ROBINSO R.,

ATTORNEY.

United States Patent 3,185,224 APPARATUS FOR DRILLING BOREHOLES Leon H. Robinson, Jrz, Houston, Tex, assignor, by mesne assignments, to Esso Production Research Company, Houston, Tex, a corporation of Delaware Filed May 27, 1963, Ser. No. 283,173 2 Claims. (Cl. 175-2) This invention relates to drilling boreholes in the earth, and more particularly to expediting the drilling of boreholes by means of explosive charges.

It has been known to use explosive charges to assist in the drilling of boreholes. One technique that has been used includes suspending a shaped charge from a drilling bit, lowering the bit to the bottom of a borehole, and detonating the shaped charge to blast an elongated, tapering hole in the bottom of the borehole. The apparatus used in this technique provides a central opening in the bit so that the charge extends therefrom through the opening. The technique has had but little use because the force of the explosive usually damages the bit bearings. However, it is highly desirable to use explosives in connection with conventional drilling techniques, particularly when drilling operations are being conducted through very hard formations such as chert. Usually, conventional bits penetrate chert only with great difiiculty and at an uneconomical rate of speed. Explosives not only dislodge portions of such hard formations, but also crack and loosen a large portion of the formation below the bottom of the borehole so that the task of the bit is made considerably easier.

In accordance with the teachings of the present in vention, there is provided an elongated drill string having an annular drilling head including a drilling bit at the lower end thereof. The drilling head is provided with a bore having a predetermined minimum diameter so as to act as a choke. An elongated explosive charge housing having a diameter only slightly less than the diameter of the choke encloses a non-directional explosive charge at the lower end thereof. A firing cap or squib is provided at the upper end of the housing, along with a differential pressure responsive firing means to fire the squib. A long, relatively slow-burning line explosive having a burning time of at least 4 seconds connects the squib to the explosive charge. The housing is pumped down the drill string and, as it passes through the drilling head, the differential pressure thereacross at that time actuates the firing means to fire the squib. The time delay before the explosive charge is detonated is suflicient for the housing to pass through the drilling head and drop to the bottom of the borehole. After the explosive charge is detonated, the resulting detritus is circulated out of the well bore and conventional drilling is commenced.

Objects and features of the invention not apparent from the above discussion will become evident upon consideration of the following detailed description of the invention, wherein:

FIGS. 1A and 1B, taken together, are a cross-sectional view of an embodiment of the invention;

FIG. 2 is a sectional view taken along section 2-2 of FIG. 1A; and

FIGS. 3, 4, and 5 are schematic, cross-sectional views of a well installation illustrating the use of the invention in a well drilling operation.

With reference now to FIGS. 1A, 1B, and 2, there is shown an elongated housing member or capsule 13 enclosing a nondirectional explosive charge 19 at the lower end thereof. The nondirectional explosive charge may be of either a brisant or an unbrisant explosive material such as TNT, RDX, PETN, ammonium nitrate, or com- 'ice binations of any two or three of these. Disposed in the explosive charge 19 at the upper end thereof is a firing means therefor, such as a blasting cap 21.

At the upper end of the housing 13 there is connected apparatus for detona-ting blasting cap 21 responsive to differential pressure of predetermined magnitude between the interior and exterior of a drill string. This apparatus comprises an outer housing section 11 of housing 13, an elongated inner sleeve 47 having a reduced diameter portion at the upper end thereof, and an enlarged diameter portion 48 at the lower end thereof. This elongated member acts as a piston cylinder for piston member 43, which piston member is provided with a piston ring 45. The upper face of the piston member 43 is exposed to the pressure around the exterior of the housing. The enlarged diameter portion 48 has a circular plate 37 connected to piston 43 by connecting rod 41. A firing pin 27 having a plate 33 connected to the upper end thereof is disposed in the lower end of the firing apparatus housing and extends through a wall 28. The firing pin 27 is placed above an igniter squib 25 held in position in an opening in the wall 24. The firing pin is held in position by a shear pin 29. A compression spring 35 is disposed between plates 37 and 33. A port 31 provides fluid communication between the annular space 32 and the interior of portion 48. A small diameter, elongated tubular member 22 extends from annular space 32 down a substantial portion of the housing 13 and passes through the housing wall as shown. A small rubber plug 20 may be more or less loosely fitted into tubular member 22 to prevent intrusion of drilling fluid into the tubular member 22 while the housing is passing down the well bore. Thus, the piston 43 and plate 37 will move downwardly responsive to differential pressure between the upper end and a location near the lower end of housing 13. When such differential pressure exists, plug 20 will be easily blown out of tubular member 22.

Connected between igniter squib 25 and blasting cap 21 is an elongated line explosive 23. The burning time of this line explosive is at least 4 seconds.

With reference now to FIGS. 3, 4, and 5, there is shown a drill pipe 5 disposed within a bore hole 1. The drill pipe 5 has a drilling head 7 at the lower end thereof, which head includes a drilling bit, here indicated to be a diamond bit such as is often used in drilling through extremely hard earth formations. A roller-type rock bit may be used provided that there is an annular opening therethrough, as will become evident below.

As shown, the drilling head is annular in shape and is provided with an opening therethrough which acts as a choke. The opening preferably is only slightly larger than the maximum diameter of capsule 13 and firing apparatus housing. The length of the portion of the drilling head which is of uniform diameter should be somewhat less than the distance from the upper end of housing section 11 to the point on the housing 13 at which the tubular member 22 extends through the housing so that the differential pressure existing between the bore of the drill pipe 5 and the exterior of the drill pipe can be applied to the piston in the firing device.

The operation of the apparatus described above is as follows. Let it be assumed that the drilling operation has proceeded in accordance with conventional techniques until a formation has been reached which is extremely hard and through which the drilling bit is making but little progress. At this point the drilling head shown in the apparatus, or an equivalent device, will be affixed to the lower end of the drill pipe if it is not already thereon. An apparatus such as is shown in FIGS. 1A and 1B is thereupon injected into the drill pipe and pumped down the drill pipe in the arming fluid. When the housing is 1 reaches the lower end of the drill pipe so that the lower end thereof protrudes through the bore 9 as shown in FIG. 3, the differential pressure appearing across piston 43 and plate 37 will cause a compressive force to be exerted on the spring 35, which in turn will be transmitted to firing pin 27. Shear pin 29 will shear almost immediately to fire the igniter squib 25. The capsule 13 will drop out of the lower end of the drill pipe as shown in FIG. 4. After a time interval determined by the burning time of fuse or line explosive 23, the line explosive 23 will ignite blasting cap 21 to detonate explosive charge 19 as shown in FIG. 5. The detritus resulting therefrom will consist of earth particles and the remainder of the apparatus shown in FIGS. 1A and 1B. This detritus will then be circulated up the annulus around the well bore. Another apparatus, which is shown in FIGS. 1A and 1B, may be circulated down the well at appropriate intervals, such as 400 to 1000 feet behind the first apparatus. A second such apparatus is designated by the reference numeral 13:: in FIGS. 4 and 5. This apparatus will be fired and detonated in the same manner as described above.

Each explosive charge injected down the well bore and through the bottom of the drill pipe 5, as described above, will scab off a portion of the lower end of the borehole.

After a desired number of such explosive charges have been detonated, the drill pipe may be lowered and conventional drilling resumed. It will be found that the drilling operation will be considerably expedited by virtue of the fact that the formation has been cracked and fissured for a considerable distance below the bottom of the well bore.

The above description and examples of the invention are for the purpose of illustration, and it is not intended that the invention be limited except by the scope of the appended claims.

What is claimed is:

1. Drilling apparatus comp-rising:

an annular drill pipe having an annular drilling head at the lower end thereof with a reduced diameter choket erethrough;

an elongated housing having a maximum outside diami means including a line explosive connecting said igniter squib to said explosive charge adapted to detonate said explosive charge at least 4 seconds after firing of said igniter squib.

2. Drilling apparatus comprising:

an annular drill pipe having an annular drilling head at the lower end thereof with a reduced diameter choke 'therethrough; 7

an elongated housing having a maximum outside diameter slightly less than the diameter of said choke so as to pass through and out of the lower end of the drilling head;

a nondirectional explosive charge in the lower end of said housing;

an igniter squib in the upper end of said housing;

firing means in said housing for firing said igniter squib responsive to differential hydrostatic pressure of predetermined magnitude between the interior and exterior of said drill pipe;

means including a line explosive connecting said igniter squib to said explosive charge adapted to detonate said explosive charge at least 4 seconds after firing of said igniter squib;

said firing means comprising a wall at the upper end of said housing above said squib, an elongated piston cylinder in said housing above said wall, opening to the xterior of said housing at the upper end thereof, a firing pin extending from said cylinder through said wall immediately above said squib, means including a shear pin holding said firing pin in position relative to said wall, and a piston in said piston cylinder adapted for longitudinal movement in said cylinder;

a spring between said firing-pin and said cylinder for exerting downward force on said firing pin upon downward movement of said piston; and

means including an elongated tube for providing fluid communication from the lower end of said cylinder beneath said piston to a location at the exterior of the lower portion of said housing whereby differential pressure between the upper end of said housing and said location is exerted across said piston.

References Cited by the Examiner UNITED STATES PATENTS 2,679,380 5/54 Sweetman 10220 2,749,840 6/56 Babcock 102-20 2,869,825 1/59 Crawford 175-2 2,923,239 2/ Andrew et al 10227 3,022,729 2/62 Robinson 2 X 3,118,503 1/64 Friedman et al 175-2 3,130,797 4/64 Johnson 175--2 CHARLES E. OCONNELL, Primary Examiner. 

1. DRILLING APPARATUS COMPRISING: AN ANNULAR DRILL PIPE HAVING AN ANNULAR DRILLING HEAD AT THE LOWER END THEREOF WITH A REDUCED DIAMETER CHOKE THERETHROUGH; AN ELONGATED HOUSING HAVING A MAXIMUM OUTSIDE DIAMETER SLIGHTLY LESS THAN THE DIAMETER OF SAID CHOKE SO AS TO PASS THROUGH AND OUT OF THE LOWER END OF THE DRILLING HEAD; A NONDIRECTIONAL EXPLOSIVE CHARGE IN THE LOWER END OF SAID HOUSING; AN AGNITER SQUIB IN THE UPPER END OF SAID HOUSING; FIRING MEANS IN SAID HOUSING FOR FIRING SAID IGNITER SQUID RESPONSIVE TO DIFFERENTIAL HYDROSTATIC PRESSURE OF PREDETERMINED MAGNITUDE BETWEEN THE INTERIOR AND EXTERIOR OF SAID DRILL PIPE; AND MEANS INCLUDING A LINE EXPLOSIVE CONNECTING SAID IGNITER SQUIB TO SAID EXPLOSIVE CHARGE ADAPTED TO DETONATE SAID EXPLOSIVE CHARGE AT LEAST 4 SECONDS AFTER FIRING OF SAID IGNITER SQUIB. 